Transmission for vehicle

ABSTRACT

An All-Terrain Vehicle (ATV) having a transmission assembly featuring an improved gear arrangement is disclosed. The transmission assembly includes a first gear having a central opening, the first is disposed such that the axis of the fork rod of the transmission passes through the central opening of the first gear.

CROSS REFERENCES TO RELATED APPLICATIONS

The present Utility Patent Application claims priority from U.S. Provisional Patent Application No. 60/746,144 filed May 1, 2006, the content of which is incorporated herein by reference. The present Utility Patent Application is also related to U.S. Application Publication No. 2003/0221893 A1 published Dec. 4, 2003, the content of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to transmissions for vehicles and to transmission gear arrangements in particular.

BACKGROUND OF THE INVENTION

Taking All-Terrain Vehicle (ATV) as an example, typically, an ATV includes front wheels and rear wheels suspended on a front end and on a rear end, respectively, of a body frame. Handlebars and a seat are mounted on the frame. A power unit such as an engine is also mounted on the frame and generates the power required to propel the ATV. A transmission is provided to transfer the power generated by the engine to the front wheels, the rear wheels or both the front and rear wheels to drive the ATV.

Conventional transmission of ATV have a reverse idle gear and shaft disposed in a transmission housing wherein the shaft extends the full length of the transmission casing. The reverse idle gear shaft is typically supported on the left and the right ends of the transmission casing and extend fully therebetween. This typical gear arrangement requires additional space thereby increasing the size of the transmission casing and adding weight.

U.S. Pat. No. 6,799,485 discloses an engine/transmission assembly wherein the reverse idle gear shaft of the transmission gear mechanism is disposed within the transmission chamber and is supported on one side by a cover separating the transmission chamber from the crankcase thereby reducing weight. This arrangement only partially reduces the weight and size of the transmission and complicates the assembly of the components of the transmission.

Thus, there is a need for an improved transmission gear arrangement that alleviates some of the drawbacks of prior art transmission.

STATEMENT OF THE INVENTION

One aspect of the present invention is to provide a transmission assembly having an auxiliary gear arranged in alignment with the fork rod.

Another aspect of the present invention is to provide a transmission assembly comprising a housing; a primary shaft and a secondary shaft; a plurality of gears mounted on the primary shaft and a plurality of gears mounted on the secondary shaft, the plurality of gears being disposed within the housing; at least one fork rod having an axis, the at least one fork rod being supported by the housing; at least one shift fork slidably mounted on the at least one fork rod and adapted to move along the axis of the fork rod, at least one shift fork being operatively connected to one of the plurality of gears to effect gear change; and a first gear having a central opening; the axis of the fork rod passing through the central opening of the first gear.

Another aspect of the present invention provides that one end of the fork rod is supported by a bushing mounted to the transmission housing and the first gear is supported on an outer portion of the bushing.

Another aspect of the present invention provides that a bearing is supporting the first gear on the bushing.

A further aspect of the present invention provides that the first gear includes an axis of rotation, wherein the axis of rotation of the first gear is co-axial with the axis of the fork rod.

Another aspect of the present invention provides that the first gear is offset relative to the axis of the fork rod.

Another aspect of the present invention is to provide a transmission assembly comprising a housing; a primary shaft and a secondary shaft; a plurality of gears mounted on the primary shaft and a plurality of gears mounted on the secondary shaft, the plurality of gears being disposed within the housing; at least one fork rod having an axis, the at least one fork rod being supported by the housing via at least one support bushing; at least one shift fork slidably mounted on the at least one fork rod and adapted to move along the axis of the fork rod, at least one shift fork being operatively connected to one of the plurality of gears to effect gear change; and a reverse gear having a central opening; the axis of the fork rod passing through the central opening of the reverse gear, the reverse gear being supported by the at least one support bushing.

Another aspect of the present invention is to provide an ATV comprising: a frame; at least four wheels suspended from the frame, at least two of which are front wheels, and at least two of which are rear wheels; a suspension connecting the wheels to the frame; a straddle-type seat supported by the frame; an engine/transmission assembly mounted to the frame and operatively connected to at least one of the wheels for driving the at least one of the wheels; the transmission comprising: a housing; a primary shaft and a secondary shaft; a plurality of gears arranged on the primary shaft and a plurality of gears arranged on the secondary shaft, each of the pluralities of gears being disposed within the housing; at least one fork rod having an axis, the at least one fork rod being supported by the housing; at least one shift fork slidably mounted on the at least one fork rod so as to move relative to the axis of the fork rod, the at least one shift fork being operatively connected to one of the gears to effect a change of gears; and a first gear having a central opening, the first gear disposed within the housing such that the axis of the fork rod passes through the central opening of the first gear.

Embodiments of the present invention each have at least one of the above-mentioned aspects, but not necessarily have all of them.

Additional and/or alternative features, aspects and advantages of the embodiments of the present invention will become apparent from the following description, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention as well as other aspects and further features thereof, reference is made to the following description which is to be used in conjunction with the accompanying drawings, where:

FIG. 1 is a perspective view of an all-terrain vehicle in accordance with an embodiment of the invention;

FIG. 2 is a side elevational view of the all-terrain vehicle illustrated in FIG. 1 with the outer shell of the vehicle shown in dotted lines;

FIG. 3 is a cross-sectional view of an embodiment of an engine/transmission assembly suitable for used with the all-terrain vehicle illustrated in FIGS. 1 and 2;

FIG. 4 is a perspective view of selected internal components of the embodiment of the transmission illustrated in FIG. 3;

FIG. 5 is a second perspective view of selected internal components of the transmission illustrated in FIG. 4;

FIG. 6 is a schematic cross-sectional view of selected internal components of the transmission in accordance with an embodiment of the invention;

FIG. 6A is a schematic partial cross-sectional view of selected internal components of the transmission in accordance with another embodiment of the invention;

FIG. 7 is a another perspective view of selected internal components of the transmission illustrated in FIG. 4;

FIG. 8 is a another perspective view of selected internal components of the transmission illustrated in FIG. 4;

FIG. 9 is a further perspective view of selected internal components of the transmission illustrated in FIG. 4;

FIG. 10 is a top plan view of the gear arrangement of the transmission when in the park position:

FIG. 11 is a perspective view of a selected internal component of the transmission illustrated in FIG. 4;

FIG. 12 is an exploded perspective view of the selected internal component illustrated in FIG. 11; and

FIG. 13 is a perspective view of a selected internal component of the transmission in accordance with another embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENT(S)

FIG. 1 illustrates an ATV 10 in accordance with one specific embodiment of the invention. The vehicle 10 has a pair of front wheel assemblies 12 and a pair of rear wheel assemblies 13. The vehicle 10 includes a straddle seat 17 positioned over the engine/transmission assembly 34 (FIG. 2) and a steering system which includes a steering member in the form of handlebars 20 to transfer steering commands of the rider to the front wheel assemblies 12. The vehicle 10 also features a front bumper 14, a front carriage rack 15 and a rear carriage rack 16 disposed over the bodywork 22. The bodywork 22 includes front and rear fenders 24 and 26 respectively, footrests 25 on either side of the vehicle 10 and joining the front end rear fenders 24 and 26, and fairing elements 27 and 28 covering the front and rear portion of the vehicle 10 respectively.

As illustrated in FIG. 2, the ATV 10 includes a frame 30 that supports and houses the engine/transmission assembly 34 positioned between the front wheels assemblies 12 and the rear wheel assemblies 13. The front wheel assemblies 12 are connected to the front portion of frame 30 via a front suspension system including shock absorber/coil spring assemblies 18 disposed on both sides of frame 30. The rear wheel assemblies 13 are connected to the rear portion of frame 30 via a rear suspension system including shock absorber/coil spring assemblies 19. The engine/transmission assembly 34 includes an engine 36 directly connected to a transmission 38. The transmission housing may be integrated, partially integrated with the casing of engine 36. The transmission 38 includes two sub-transmissions; a continuously variable transmission (CVT) 41, and a geared sub-transmission 43, the moving components of which are enclosed within a transmission casing or housing 39. The CVT 41 is operatively connected to the geared sub-transmission 43 to transmit engine torque. The engine torque is transmitted from the geared sub-transmission 43 to the front and rear wheels assemblies 12 and 13 via the driving shafts 40 and 42 and provide motive power to the ATV 10. While the ATV 10 illustrated is all-wheel drive, the ATV 10 may be of a front wheel or rear wheel drive variety.

FIG. 3 illustrates the engine/transmission assembly 34 in which the engine 36 is a single cylinder, internal combustion engine associated with a continuously variable transmission (CVT) 41. However, the engine/transmission assembly 34 should not be limited to a single cylinder. Instead, the features of the present invention may be applied to any type of internal combustion engine, as would be appreciated by those skilled in the art. For example, the features of the present invention may be applied to a multiple cylinder, in-line, V-type, or opposed cylinder engine without deviating from the scope of the present invention. Furthermore, while the present invention includes a CVT for use with a single cylinder engine, those skilled in the art would readily appreciate that the CVT could be easily used with any other type, style, or size of internal combustion engine. Moreover, while a CVT is preferred for use with the engine of the present invention, it would be readily appreciated by those skilled in the art that the standard clutch system could be substituted for the CVT without deviating from the scope of the present invention. In addition, while the engine/transmission assembly 34 has been specifically designed for use with an ATV, which is the preferred use for the present invention, the present invention is not limited to use on ATVs. The present invention may be used in any other suitable vehicle type, including scooters, motorcycles, karts, and other suitable vehicles.

As shown in FIG. 3, the engine 36 includes a cylinder 50, a piston 52 slidably mounted within the cylinder 50, a crankshaft 54, and a connecting rod 56 interconnecting the piston 52 and the crankshaft 54. In the illustrated embodiment, the crankshaft 54 is mounted transversely to the centerline 60 of the engine 36. The engine 36 may be provided within any suitable fuel delivery system without departing from the scope of the present invention (e.g. carburetor or fuel injection system).

As shown in FIG. 3, the CVT 41 includes a drive pulley 62 and a driven pulley 64. The drive pulley 62 is fixedly connected to the crankshaft 54 such that torque is transmitted from the crankshaft 54 to the drive pulley 62. A continuous belt 66 operatively connects the drive pulley 62 to the driven pulley 64 to permit torque transfer from the drive pulley 62 to the driven pulley 64. The driven pulley 64 is fixedly connected to an input shaft 68 of the geared sub-transmission 43. The input shaft 68 is drivingly engaged with an output shaft 70 that is drivingly engaged with the driving shafts 40, 42 through a bevel gear assembly 72, 73. In cases where the engine 36 is installed in the vehicle so that the transmission shafts 68 and 70 and the crankshaft 54 of the engine are parallel to the longitudinal axis of the vehicle, no bevel gear is necessary. Thus, torque from the crankshaft 54 is transmitted from the drive pulley 62 to the driven pulley 64 via the belt 66, from the driven pulley 64 to the transmission input shaft 68, from the input shaft 68 to the output shaft 70, from the output shaft 70 to the driven shaft 40 via bevel gear assembly 72, 73, and from the driven shafts 40, 42 to the front wheel assemblies 12 and rear wheel assemblies 13 of the ATV 10. In the present application, the geared portion of the transmission is identified as a sub-transmission however, the geared sub-transmission 43 is not necessarily a sub-element of a transmission assembly and may be a transmission assembly of it own.

FIG. 4 illustrates the main internal components of the geared sub-transmission 43 removed from the transmission casing. The main internal components of the sub-transmission 43 include the output shaft 70 supported by a casing bearing 74, the output shaft 70 having a shift gear 75 and two idle gears 76 and 77 mounted on the output shaft 70 on opposing sides of the shift gear 75; an input shaft 68 having one shift gear 78 and a idle gear 79 (FIG. 5) mounted thereon. As is well known in the field of automotive transmissions, shift hubs having no circumferential teeth may be used instead of the shift gears 75 and 78 as gear engaging elements for engaging the sides of the idle gears to effect gear changes. As illustrated, a pair of shift forks 82 and 84 are operatively connected to the shift gears 75 and 78 respectively. The shift forks 82 and 84 are slidably mounted onto a fork rod 80 supported by the transmission casing. A shift drum 86 including a pair of grooves 88 and 90 operatively connected to shift forks 82 and 84 via follower 110, 111 that are received within a corresponding grooves 88 and 90 of the shift drum 86. A shifting assembly 91 has a shifting shaft 92 extending outwardly from the transmission casing so that it can be operatively engaged at a splined end 95 with a gear selector in the form of a handle or a foot peg that can be actuated by an ATV operator to shift gears. In this embodiment, the gearshift or gear shifting mechanism 175 includes the shift drum 86 and the shift fork assembly. The shifting assembly 91 is operatively connected to the gearshift 175 to transfer shifting commands from the operator to the gears themselves and effect gear changes. The shifting assembly 91 includes the shifting shaft 92 having a segment gear 93 rotatably supported at one end thereof. The teeth of the segment gear 93 are operatively engaged with the teeth of the toothed wheel gear 94 of the shift drum 86. As illustrated, the shifting assembly 91 is disposed parallel to the shifting drum 86 thereby minimizing the axial length of the shift drum compared to a shifting assembly disposed directly at the end of the shift drum. The segment gear 93 performs the function of actuating the shift drum 86 to impart rotation of the shift drum 86 in one direction or the other. Instead of a segment gear, other actuators could be operatively connected to the shift drum 86, such as bi-directional pawls engaging the toothed wheel gear 94 or a hub on the shift drum 86. In a specific embodiment, a shift gate such as that disclosed in US Pat. Application Publication No. 2004/0002399 A1 (which incorporated herein by reference) may be used instead of a shift drum to transfer the shifting commands from the operator to the gears themselves and effect gear changes.

FIG. 5 illustrates the input shaft, the output shaft, the shift forks 82 and 84, and an auxiliary gear 96 in isolation from other internal components of the transmission 38. In a specific embodiment, the auxiliary gear 96 is used as the reverse gear. The auxiliary gear 96 may also serve to drive auxiliary components such as an auxiliary power take off shaft, a pump, etc. The auxiliary gear 96 is mounted on a bearing 102 (FIG. 4) provided on the outer portion of the supporting bushing 104 of the fork rod 80 such that the auxiliary gear 96 can rotate freely relative to the supporting bushing 104 or the fork rod 80. Depending on the design of the supporting bushing 104, the axis of rotation of the auxiliary gear 96 may coincide with the center line of the fork rod 80 or not. As illustrated in FIG. 6, the inner cavity of the supporting bushing 104 is offset relative to the axis of rotation 106 of the auxiliary gear 96 such that the center line 108 of the fork rod 80 does not coincide with the axis of rotation 106 of the auxiliary gear 96. The flexibility of design of the supporting bushing 104 provides more freedom of design for the positioning and various parameters of the auxiliary gear 96 (diameter, pitch, number of teeth, etc.) as well as adjacent gears 76 and 100. Supporting the auxiliary or reverse gear 96 on a bearing 102 which is located on the outer portion of the supporting bushing 104 of the fork rod 80 eliminates the need for a specific supporting shaft for the reverse gear as is typically used in gearboxes. As illustrated in FIG. 6A, the fork rod 80 may be supported directly on the inner cavity 168 of a protrusion 170 of the housing 39 whereas the bearing 102 of the auxiliary or reverse gear 96 is supported on the outer portion of the protrusion 170. Similarly, the axis of rotation of the auxiliary gear 96 may or may not coincide with the center line of the fork rod 80. Thus, a gearbox having a reverse or auxiliary gear 96 positioned in the vicinity of the center line 108 of the fork rod 80 yet not necessarily coaxial with the center line 108 may be lighter and more compact than typical gearboxes. In the specific embodiment illustrated in FIG. 5, the auxiliary/reverse gear 96 is coaxial with the center line 108 of the fork rod 80 and is positioned between the gear 100 of the input shaft 68 and idle gear 76 of output shaft 70.

With reference to FIG. 5, the shift gear 78 is operatively coupled the input shaft 68 for common rotation through splines 98 on the inner surface of the shift gear 78 and the outer surface of the input shaft 68. The splines 98 prevent relative rotational movement between the shift gear 78 and the input shaft 68 while permitting relative axial movement therebetween. The fork 84 is engaged within a recess of the shift gear 78 and is thus adapted to selectively move the shift gear 78 along the input shaft 68 between a first position engaging the idle gear 79 and a second position disengaged from the idle gear 79. The idle gear 79 is mounted on the input shaft 68 adjacent the shift gear 78 using a bearing (not shown) such that the idle gear 79 can rotate relative to the input shaft 68. The input shaft 68 also includes a gear 100 that is machined directly thereon. This gear 100 may also be pres-fitted onto the input shaft 68 or simply fixed to the input shaft 68 so that it rotates in unison with the input shaft 68.

The output shaft 70 also includes a shift gear 75 operatively coupled to the output shaft 70 for common rotation about the output shaft axis through axially aligned splines on the inner surface of the shift gear 75 and the outer surface of the output shaft 70 (not shown). The splines prevent relative rotational movement between the shift gear 75 and the output shaft 70 while permitting relative axial movement therebetween. The fork 82 is engaged within a recess of the shift gear 75 and is thus adapted to selectively move the shift gear 75 between a first position engaging the idle gear 77, a second position engaging the idle gear 76, and a third position wherein the shift gear 75 is engaging neither of the idle gears 76 and 77. The idle gears 76 and 77 are mounted on the output shaft 70 on opposing sides of the shift gear 75 using bearings (not shown) such that the idle gears 76 and 77 can rotate relative to the output shaft 70. The output shaft 70 includes a bevel gear 73 that is drivingly interconnected with the gear 72 provided on the output shaft 40 as illustrated in FIG. 3.

In operation, the shift gears 75 and 78 of the input shaft 68 and of the output shaft 70 are controlled by shift forks 82 and 84 to change the gear ratio of the transmission. Specifically, the shift fork 82 is operatively engaged with the shift gear 75 on the output shaft 70 and its follower 110 is engaged within the corresponding groove 90 provided of the shift drum 86. The shift fork 84 is engaged with the shift gear 78 on the input shaft 68 and its follower 111 is engaged within the corresponding groove 88 provided of the shift drum 86. Thus, a rotation of the segment gear 93 of the shifting assembly 91 imparts a rotational movements of the shift drum 86. The grooves 88 and 90 impart lateral motion to the shift forks 82 and 84 which in turn move the shift gears 75 and 78 along their respective shaft according to a pre-determined sequence defined by the pattern of the grooves 88 and 90. In this specific embodiment, the shift drum 86 includes five positions: park, reverse, neutral, high, and low. Obviously, the shift drum 86 may provide for more or less positions depending on the number of gears and the specific requirements of the vehicle.

As illustrated in FIG. 7, the shift drum 86 is supported on one side by a first shaft portion 115 extending into a bearing within a cavity of the transmission casing (not shown) and on the other side by a second support shaft portion 113 (FIG. 8) extending into a bearing within a bearing shield 116 mounted on the transmission casing. A selector wheel 118 is connected to the shift drum 86 such that the gear positions are specifically defined. The selector wheel 118 is fixed to the shift drum 86 and follows the shift drum 86 through its rotation. An indexing lever 120 is pivotally mounted onto the bearing shield 116 and biased into engagement with the selector wheel 118 by a spring 122. The indexing lever 120 interacts with the selector wheel 118 to enable identification of the five possible positions. The selector wheel 118 has five recesses around the periphery thereof corresponding to the five positions of the shift drum 86. The indexing lever 120 engages within a selected one of the recesses, as the shift drum 86 is rotated via its toothed wheel gear 94 to mark one of the five positions. A park locking lever 125 is rotatably mounted to the transmission casing through a supporting shaft 126 extending into a bearing within a cavity of the transmission casing (not shown).

FIG. 8 is a perspective view from the opposite side of FIG. 7 with the bearing shield 116 and the indexing lever 120 removed to better show the park locking lever 125 operatively connected to the shift drum 86. As shown, the shift drum 86 includes a second support shaft portion 113 extending into a bearing within the bearing shield 116 (FIG. 7) which is coaxial with the shaft portion 115, thereby defining the axis of rotation of the shift drum 86. The shift drum 86 includes a guiding member in the form of an eccentric knob 128 offset relative to the axis of rotation of the shift drum 86. The eccentric knob 128 is fixed to the shift drum 86 and rotates with the shift drum 86 when the latter is rotated via its toothed wheel gear 94. As illustrated in FIGS. 8 and 9, the park locking lever 125 includes a body 134 having an elongated aperture 130 that fits onto the eccentric knob 128, is operatively connected thereto and acts as a follower member. A toothed segment 132 is provided on the outer edge of the body 134 which is aligned with the teeth of the idle gear 79. In operation, when the shift drum 86 is rotated to the park position, the eccentric knob 128 rotates with the shift drum 86 which in turn imparts a motion to the body 134 of the park locking lever 125 such that toothed segment 132 engages the teeth of the idle gear 79 to lock idle gear 79 thereby prevent any further rotation of the idle gear 79. However, the elongated aperture 130 is designed to provide extended room for the eccentric knob 128 to rotate within the elongated aperture 130 while imparting little movement to the park locking lever 125 such that the toothed segment 132 remains disengaged from the idle gear 79 throughout the rotation of the shift drum 86 along the reverse, neutral, high, and low positions. The eccentric knob 128 defines a pattern about the first axis of rotation for the park locking lever 125 to follow. The eccentric knob 128 moves the park locking lever 125 towards the idle gear 79 in the final segment of rotation of the shift drum 86 between the reverse position and the park position. The toothed segment 132 of the park locking lever 125 is disengaged from the idle gear 79 when the shift drum 86 is rotated away from the park position. The park locking lever 125 is coupled to the eccentric knob 128 and follows the motion of the eccentric knob 128 through the entire path of the eccentric knob 128. The park locking lever 125 is therefore guided by the shift drum 86 as the latter rotates.

In a particular embodiment, the park locking lever 125 may be provided with a pin or knob which is inserted into a groove located on the shift drum 86 designed to guide the park locking lever 125 such that its toothed segment 132 will engage the idle gear 79 only in the park position.

As illustrated in FIG. 10, with the idle gear 79 locked by the toothed segment 132 of the park locking lever 125, the shift gear 75 (which is coupled to the output shaft 70 through axially aligned splines) is also immobilized. The output shaft 70 and the driving shafts 40, 42 (connected through the bevel gear 73) are thus locked.

Referring back to FIG. 4, the shifting assembly 91 is operatively connected to the shift drum 86 through the segment gear 93 engaging the toothed wheel gear 94 of the shift drum 86. Therefore rotation of the segment gear 93 is translated into a corresponding rotation of the shift drum 86. This in turn actuates the shift forks 80 and 82 to change the coupling of the gears on the input and output shafts 68 and 70. The shifting assembly 91 is positioned within the transmission housing 39 with the exception of the splined end 95 of the shifting shaft 92 which protrudes outside the transmission housing 39. The shifting assembly 91 is therefore protected from the environment.

As illustrated in FIG. 11, the shifting assembly 91 includes a lever 140 fixedly connected to the shifting shaft 92 that rotates in unison therewith. The lever 140 has a first portion 142 extending perpendicular to the shifting shaft 92 and a second portion 144 extending parallel to the shifting shaft 92. The shifting assembly 91 also includes a torsion spring 152 installed onto a sleeve portion 154 of the segment gear 93. With reference to FIG. 12, the torsion spring 152 is a coil spring wherein the extremities are bent to extend perpendicular to the coil within a single plane. The inside diameter of the torsion spring 152 corresponds approximately to the outside diameter of the sleeve portion 154 of the segment gear 93. The segment gear 93 is fixedly connected to the sleeve portion 154 which has an inside diameter corresponding to the outside diameter of the shifting shaft 92. The sleeve portion 154 including the segment gear 93 are rotatably mounted onto the shifting shaft 92. The segment gear 93 further includes a seat 156 projecting from one edge of an opening 146 in the central portion of the segment gear 93 and extending parallel to sleeve portion 154. The end of the second portion 144 of the lever 140 includes a pair of recesses 148 and 150 adapted to receive the extremities 160 and 162 of the torsion spring 152.

Referring back to FIG. 11, the sleeve portion 154 of the segment gear 93 is inserted into the torsion spring 152. The shifting shaft 92 is inserted into the sleeve portion 154 of the segment gear 93 such that the second portion 144 of the lever 140 extends towards the segment gear 93. The projecting seat 156 of the segment gear 93 extends towards the lever 140 as illustrated. The recesses 148 and 150 are aligned with the sides of the projecting seat 156. The extremities 160 and 162 of the torsion spring 152 abut against both the recesses 148 and 150 and the projecting seat 156. The rotational movement of the shifting shaft 92 imparted by with a gear selector connected to the splined end 95 is thus transferred to the segment gear 93 through the torsion spring 152.

In operation, when the operator of the vehicle is selecting a gear position, the shifting shaft 92 is rotated clockwise or counter clockwise. In the event the shifting shaft 92 is rotated clockwise as indicated by the arrow B, the lever 140 rotates and pushes on the extremity 160 of the torsion spring 152 positioned within the recess 148. The torsion spring 152 transfers the pushing force to its other extremity 162 which abuts against the side of the projecting seat 156. This imparts rotational motion to the segment gear 93 which in turn rotates the shift drum 86 to effect gear selection. Similarly, in the event the shifting shaft 92 is rotated counter clockwise (in the opposite direction to the one indicated by the arrow B), the lever 140 rotates and pushes on the extremity 162 of the torsion spring 152 positioned within the recess 150. The torsion spring 152 transfers the pushing force to its other extremity 160 which abuts against the side of the projecting seat 156. This imparts rotational motion to the segment gear 93 which in turn rotates the shift drum 86 in the other direction to effect gear selection.

In the operation of the vehicle 10, it is possible that the shift gears 75 or 78 may be difficult to engage to or disengage from their adjacent gears should for instance the engaging members of adjacent gears be misaligned or should the friction forces between two coupled gears be such that the force required to the shift gears 75 or 78 places undue stress on the shift forks 82, 84. The shifting assembly 91 is provided to alleviate some of these locking problems. If a gear change is difficult to effect, when the operator applies a force to the gear selector connected to the splined end 95 of the shifting shaft 92 thereby applying a torque to the shifting shaft 92, the lever 140 will push on the corresponding extremity 160 or 162 of the torsion spring 152. However the other extremity 160 or 162 of the torsion spring 152 will only apply a limited force to the seat 156 while a portion of the applied force or torque will be stored in the spring 152 itself through the prying apart the two extremities 160 or 162 (proportional to the spring rate or spring constant k of the torsion spring 152). The excess force or energy received through the gear selector is therefore stored temporarily in the shifting assembly 91 and more specifically in the torsion spring 152 to protect the internal components of the transmission from excessive force. This energy is released through the internal components of the transmission if the situation that made the gear change difficult to effect is eliminated or back to the gear selector through the shifting shaft 92 if the situation remains unchanged.

Similarly, the gear selector (not shown) connected to the splined end 95 of the shifting shaft 92 may be guided through a channel provided with gates or recesses corresponding to the various positions i.e. park, reverse, neutral, high, and low. The gear selector may be locked into the gates or recesses to prevent unwanted gear changes. A situation may arise where the gear selector may be moved into a gate or recess and locked into that position while the shift gears 75 or 78 are not yet engaged because of misalignment or excessive friction two coupled gears. In this instance, the shifting assembly 91 absorbs the differential displacement of the shift drum 86 relative to the locked position of the gear selector through the torsion spring 152. The energy stored in the shifting assembly 91 will be released to effect the corresponding gear change if and when the situation which made the gear change difficult to effect is eliminated.

As illustrated in FIG. 13, in another embodiment, the lever 140 may be connected to the segment gear 93 via an elastomer or rubber element 173 that can be deformed under a load and return to its initial shape once the load is removed thereby providing the energy storing capability to the shifting mechanism 91. In this particular embodiment, the elastomer or rubber element 173 is inserted onto the opening of the segment gear 93 and the second portion 144 of the lever 140 to the segment gear 93 is inserted into the elastomer or rubber element 173. In operation, when the operator of the vehicle is selecting a gear position, the shifting shaft 92 is rotated clockwise or counter clockwise. In the event the shifting shaft 92 is rotated clockwise as indicated by the arrow B, the lever 140 rotates and pushes on the elastic element 173 positioned within the recess of the segment gear 93. The elastic element 173 transfers the pushing force directly onto segment gear 93 which in turn rotates the shift drum 86 to effect gear selection. In this instance, the shifting assembly 91 absorbs the differential displacement of the shift drum 86 relative to the locked position of the gear selector through the elastic element 173. In general, any deformable elastic component could be used to connect the lever 140 to the segment gear 93 without departing from the scope of the invention.

In a further embodiment (not Shown), the function of the elastic element 173 may be replaced by two separate spring elements disposed on opposite sides of the lever 140, each spring mounted on the segment gear 93 so as to bias the lever 140 in a center position and adapted to absorb the differential displacement of the shift drum 86 relative to the locked position of the gear selector.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments and elements, but, to the contrary, is intended to cover various modifications, combinations of features, equivalent arrangements, and equivalent elements included within the spirit and scope of the appended claims. Furthermore, the dimensions of features of various components that may appear on the drawings are not meant to be limiting, and the size of the components therein can vary from the size that may be portrayed in the figures herein. Thus, it is intended that the present invention covers the modifications and variations of the invention, provided they come within the scope of the appended claims and their equivalents. 

1. A transmission assembly comprising: a housing; a primary shaft and a secondary shaft; a plurality of gears arranged on the primary shaft and a plurality of gears arranged on the secondary shaft, each of the pluralities of gears being disposed within the housing; at least one fork rod having an axis, the at least one fork rod being supported by the housing; at least one shift fork slidably mounted on the at least one fork rod so as to move relative to the axis of the fork rod, the at least one shift fork being operatively connected to one of the gears to effect a change of gears; and a reverse gear having a central opening, the reverse gear disposed within the housing such that the fork rod and the axis of the fork rod pass through the central opening of the reverse gear, at least one of the plurality of gears arranged on the primary shaft selectively engaging at least one of the plurality of gears arranged on the secondary shaft directly, and at least one of the plurality of gears arranged on the primary shaft engaging at least one of the plurality of gears arranged on the secondary shaft via the reverse gear.
 2. A transmission assembly as defined in claim 1, wherein one end of the fork rod is supported by a bushing mounted to the housing.
 3. A transmission assembly as defined in claim 2, further including a bearing supporting the reverse gear on the bushing.
 4. A transmission assembly as defined in claim 1, wherein the reverse gear has an axis of rotation that is co-axial with the axis of the fork rod.
 5. A transmission assembly as defined in claim 1, wherein the reverse gear includes an axis of rotation that is offset relative to the axis of the fork rod.
 6. A transmission assembly as defined in claim 1, wherein the reverse gear is an auxiliary gear driving an auxiliary shaft.
 7. A transmission assembly as defined in claim 1, wherein one end of the fork rod is supported by a protrusion of the housing.
 8. A transmission assembly as defined in claim 7, wherein the reverse gear is disposed on the protrusion of the housing.
 9. A transmission assembly comprising: a housing; a primary shaft and a secondary shaft; a plurality of gears arranged on the primary shaft and a plurality of gears arranged on the secondary shaft, each of the pluralities of gears being disposed within the housing; at least one fork rod having an axis disposed within the housing, the at least one fork rod being supported by the housing via at least one support bushing; at least one shift fork slidably mounted on the at least one fork rod and so as to move relative to the axis of the fork rod, the at least one shift fork being operatively connected to one of the gears to effect a change of gears; and a reverse gear having a central opening, the axis of the fork rod passing through the central opening of the reverse gear, the reverse gear being supported within the housing by the at least one support bushing, at least one of the plurality of gears arranged on the primary shaft selectively engaging at least some of the plurality of gears arranged on the secondary shaft directly, and at least one of the plurality of gears arranged on the primary shaft engaging at least one of the plurality of gears arranged on the secondary shaft via the reverse gear.
 10. A transmission assembly as defined in claim 9, wherein the reverse gear includes an axis of rotation that is offset relative to the axis of the fork rod.
 11. A transmission assembly as defined in claim 9, wherein the reverse gear includes an axis of rotation that is co-axial with the axis of the fork rod.
 12. A transmission assembly as defined in claim 9, further including a bearing mounted on the at least one bushing, the reverse gear being supported by the bearing.
 13. An All-Terrain Vehicle (ATV) comprising: a frame; at least four wheels suspended from the frame, at least two of which are front wheels, and at least two of which are rear wheels; a suspension connecting the wheels to the frame; a straddle-type scat supported by the frame; an engine/transmission assembly mounted to the frame and operatively connected to at least one of the wheels for driving the at least one of the wheels; the transmission comprising: a housing; a primary shaft and a secondary shaft; a plurality of gears arranged on the primary shaft and a plurality of gears arranged on the secondary shaft, each of the pluralities of gears being disposed within the housing; at least one fork rod having an axis, the at least one fork rod being supported by the housing; at least one shift fork slidably mounted on the at least one fork rod so as to move relative to the axis of the fork rod, the at least one shift fork being operatively connected to one of the gears to effect a change of gears; and a reverse gear having a central opening, the reverse gear disposed within the housing such that the axis of the fork rod passes through the central opening of the reverse gear, at least one of the plurality of gears arranged on the primary shaft selectively engaging at least one of the plurality of gears arranged on the secondary shaft directly, and at least one of the plurality of gears arranged on the primary shaft engaging at least one of the plurality of gears arranged on the secondary shaft via the reverse gear.
 14. An ATV as defined in claim 13, wherein the reverse gear has an axis of rotation that is coaxial with the axis of the fork rod.
 15. An ATV as defined in claim 13, wherein the reverse gear includes an axis of rotation that is offset relative to the axis of the fork rod. 